High-voltage power supplies are commonly used and well-known for powering devices which require a high DC voltage. Most high-voltage power supplies include a transformer or inductor for converting or stepping-up a relatively low DC source voltage to a relatively high DC output voltage. Components, such as the transformer or inductor, diodes, and capacitors used in high-voltage power supply circuits must be able to withstand the effects of high voltages and, thus, are often relatively large and heavy. In smaller and/or portable devices necessitating the use of a low DC voltage source, i.e., a battery supplying 5V or less, use of such large/heavy power components is prohibitive. Even where power supply size is not as much of an issue, where the high-voltage device being powered is mostly capacitive in nature, efficiently modulating the voltage across the capacitive device can be problematic. This is particularly the ease with high-frequency (up to 10 kHz or more) capacitive devices, e.g., high-speed actuators, electronic displays, etc.
There are commonly known power circuit topologies which can be used in lieu of larger power components and also address the problem of high voltage modulation. One such topology approach is the cascading (series connection) of multiple transistor switch devices to reach a desired voltage rating. However, a significant number of parts must be added (as many as ten or more cascaded switch multipliers may be required) in addition to the main power devices, possibly including high voltage drive transformers with difficult isolation requirements. An additional concern for the modulation of high voltages in capacitive devices is that of power dissipation due to parasitic capacitances across the switching devices. In a fast switching circuit, this energy is dissipated in the transistor switch at every turn-on, and can result in a substantial amount of power dissipation. Power dissipation is particularly acute in high voltage circuits where losses due to high-frequency switching activity (commonly referred to as “switching loss”) can quickly reach unacceptable levels. In addition to reducing efficiency, these losses can increase the temperature of the switching elements beyond their ratings, causing premature failure.
Converter topologies such as zero voltage switching (ZVS) and zero current switching (ZCS) address the problem of power dissipation due to switching loss; however, they have complex designs with a high part count, which adds to the size and cost of the power supply.
A boost converter is another type of high voltage power circuit topology which provides voltage gains in the range from about 20× to 50×. They are advantageous in that they are relatively small and compact; however, conventional boost converters do not fully address the problem of power dissipation due to switching losses. Additionally, because they employ high-impedance switching circuits, they are also subject to conduction losses. In order to obviate the conductive losses, additional circuitry is commonly incorporated, but at the sake of increasing the overall size and weight of the power supply.
Another common approach is to use larger switching devices that have significantly lower conduction losses, i.e., lower on-state resistance. This increases the size and cost of the power supply. Even where the high-voltage device being powered requires a relatively low supply voltage, i.e., less than about 2 kV, the components of conventional boost converters do not allow for much of a corresponding reduction in power supply size due to the additional circuitry required to mitigate the conductive losses. Nonetheless, boost circuits have been regarded as an optimal way in which to provide DC-DC voltage step-up. This is especially true for supplies where the ratio of output voltage to input voltage exceeds a factor of one hundred or more.
Other types of power circuit topologies are well-known and commonly-used to reduce the power dissipation which occurs through switching loss without greatly adding to the weight, size or mass of the power supply. One such circuit topology is a multi-stage voltage multiplier circuit which is coupled to the output side of the transformer or inductor. Another topology includes a flyback circuit. These circuits minimize conductive losses as they involve switches having very low resistance. While these circuit topologies reduce power dissipation and are not prohibitively large or heavy for use with smaller high-voltage devices, they are still too large and heavy to be provided in a form fit to accommodate miniature device applications, such as cell phone camera modules, camera flashes, etc.
Another approach to high voltage modulation involves coupling the transducer directly to a transformer. The transformer approach allows the high transducer voltage to be stepped down by the transformer turns ratio such that charging and discharging can be accomplished at low voltages. However, the size of the required transformer increases as the frequency of the charge/discharge cycle decreases. Thus, for the majority of applications in which weight, size and mass considerations are essential, the required transformer is unacceptably large.
One approach to reducing the size of the transformer or inductor (i.e., the magnetic components, generally) and, thus, the overall size and weight of the power supply in high-voltage applications, has been to use switching components having very high switching frequencies, i.e., in the range from about 200 kHz to 2 MHz. Of course, this approach presents the problem of power dissipation due to switching losses discussed above.
Notwithstanding the operational shortcomings of prior art power supplies, there are certain conventional power circuit topologies which enable relatively small power supply architectures. Examples of commercially available “miniature” DC-DC converters which employ one or more of the above approaches are as follows: EMCO High Voltage Corporation Q Series (Q50-5) converter supplying up to 5 kV output with an architecture having a volume of 0.125 in3 (approximately 2.050 mm3) and weighing 0.15 ounces (4.25 g); Gamma High Voltage Research, Inc. SM Series power supply supplying up to 3 kV and having an architecture volume of less than 1 in3 (approximately 16,400 mm3); Matsusada Precision, Inc. UP Series power supply with outputs from 100 to 500 V and having an architecture volume of 0.432 in3 (approximately 7,080 mm3) and AM Power Systems high voltage converters with outputs from 500 V to 5 kV and having an architecture volume of about 1 in3 (approximately 16,400 mm3) and weighing about 1 ounce (29 grams). While the sizes of these “miniature” power supplies are relatively small, the inventors hereof are not aware of an available power supply having an even smaller architecture, or one that could be scaled-down in size even with a substantially lower output voltage requirement, e.g., less than 2 kV.
In sum, prior art high-voltage power supply technology involves a tradeoff between size/weight and power dissipation due to switching losses. Thus, there continues to be an interest and need in developing high-voltage power supplies where size and weight efficiency is paramount without sacrificing power efficiency. As such, it would be highly beneficial to provide a high-voltage power supply made of extremely cost-effective, light-weight components which can realize ultra-miniature power supply architectures without the expected switching losses. Further, it would be highly advantageous to provide such a power circuitry topology which gives a manufacturer the flexibility in scaling the size of the power supply to the desired voltage output of the supply.